Particle size distribution is an important parameter in many processes and its accurate measurement is required for the precise and cost-effective control of the process. The measurement of particle size distribution in order to accurately control a process finds importance in industries that manufacture cement, cosmetics, pharmaceuticals and the like. A number of instruments are presently used in industry that use angular light scattering or dynamic light scattering techniques to measure particle size distribution in a liquid medium. These instruments analyze and measure the concentration of particles suspended in the liquid medium and provide a measurement that is used to adjust the process in order to correct for any irregularities in the final processed product. One such angular light scattering measurement instrument is taught in U.S. Pat. No. 5,416,580, to Trainer et al, issued May 16, 1995.
In order for these aforementioned instruments to measure correct particle size distribution, a sample representative of the processed medium to be analyzed must be extracted from the process, conditioned and applied to a measurement instrument. Conditioning disperses the particles within the suspension into a concentration value that is within the concentration requirements of the measurement technique being utilized. The concentration of particles within a typical process is generally higher than is allowed by the measurement technique being utilized and the aforementioned conditioning introduces some form of dilution to disperse the concentration. For example, in the case of instruments that employ angular light scattering techniques, multiple scattering limits the concentration to less than 0.1% of particles in suspension. In the case of dynamic light scattering, particle-to-particle interactions limit concentration to less than 3%. Particle concentrations in a processed medium, however, can be as high as 50% by volume.
Current practices utilize a mechanical device to enter the process, capture a sample of the processed medium and withdraw the sample into a dilution chamber. Diluent is pumped by a mechanical device into the dilution chamber to provide the correct ratio of sample to diluent. The now conditioned sample is circulated to the measurement instrument for analysis. Such conditioning methods and associated apparatus are taught in U.S. Pat. No. 4,496,244. to Ludwig et al, issued Jan. 29, 1985, and U.S. Pat. No. 5,439,288, to Hoffman et al, issued Aug. 8, 1995.
The presently known systems suffer from poor reliability and excessive maintenance due to the requirement for multiple seals to effect the mechanical motion of extracting the sample from the process. Additionally, such systems require many hours of maintenance in cleaning the mechanical extraction devices in order to operate efficiently.